Gas turbine engines rotate at relatively high speeds. When these engines are used to drive aircraft propellers or rotors, which generally require low speeds, gear reduction must be used. A suitable gearbox, such as a reduction gearbox, links the output of the gas turbine engine to the input of the propeller or rotor. More particularly, the reduction gearbox will lower the speed of the output of the gas turbine engine provided to the propeller or rotor.
Reduction gearboxes typically have multiple speed reduction stages, each stage adding to the overall size of the gearbox. High speed gas turbine engines are often used with reduction gearboxes having two or more stages in order to be able to reduce the very high rotational speed of the gas turbine to a relatively low speed for propeller or rotor outputs, the speed reduction being dependent on the gearbox transmission ratio. Such a reduction gearbox can have too large of a space footprint to be accommodated in close proximity to the core of the gas turbine engine. For example, brining such a reduction gearbox in close proximity to the core of the gas turbine engine would bring it in spatial conflict with components such as the air intake. The relatively large separation between the reduction gearbox and the core of the gas turbine engine can lead to larger, and therefore heavier, gas turbine engines.